When they’re humming, the fourth-line grinders represent the values of the brand: courage, tenacity, and dedication. On Saturday, when the 48-game season begins at TD Garden against the New York Rangers, their jobs will be no different than the task their coaches have always demanded.

Movement is more rampant on fourth lines. Muckers and grinders and scrappers, mostly on short-term deals, live like vagabonds in search of their next contracts.

It’s the opposite in Boston. Paille, Campbell, and Thornton are entering their third season of coexistence. It is the most consistent threesome of the Bruins’ four lines.

Last year, after Nathan Horton’s season-ending concussion Jan. 22, Milan Lucic and David Krejci were without their regular right wing. Tyler Seguin replaced the retired Mark Recchi. Benoit Pouliot was the No. 3 left wing.

Paille, Campbell, and Thornton have been together so long, it wouldn’t be a surprise if they knew each other’s answers to those security questions (mother’s maiden name, city of honeymoon, high school mascot) when passwords go forgotten.

“It helps with communication,” Thornton said. “We can read off each other a lot better without even having to talk out there most times. I know their tendencies. I’m sure it’s the same the other way. It makes life a little bit easier. I don’t have to think too much. I can just read and react off what the play’s going to be, because I know what they’re going to do.”

Paille is the speedster. The left wing is one of the team’s fastest straight-line players. Paille can pressure defensemen up the ice to delay opposing teams’ breakouts.

Campbell is the smart, speedy, and physical center. Campbell wears out opponents with his check-finishing style. He’s not afraid to drop the gloves and take on bigger fighters.

Thornton is the enforcer. Last season, Thornton fought 20 times. In even-strength situations, Thornton’s smarts, soft hands, and physical play make him one of the league’s most well-rounded heavyweights. On Jan. 10, 2012, Thornton submitted one of the team’s most dazzling goals. On a penalty shot, Thornton dangled around Winnipeg’s Ondrej Pavelec before tucking a backhander under the crossbar.

Together, their assets can make them one of the NHL’s most powerful fourth lines. Thornton has often said Paille and Campbell are good enough to be third liners elsewhere.

Their coaches and teammates are quick to recall their importance in the playoffs. During the 2010-11 postseason, they played thorough, two-way hockey. Early in Game 7 of the Stanley Cup Final, the Canucks dictated the pace. The fourth line held the fort until the other forwards gained some traction.

They could have a similar impact this season. Because of the 48-game schedule, each match should have playoff-like intensity. In such situations, the fourth line plays its best.

“I think the coaching staff has been extremely fair to us,” Campbell said. “I think they realize that the success of the team comes from everybody. [Coach] Claude [Julien] does an amazing job of using four lines. I think he recognizes that if you want to have success, the top lines are the lines you’re going to have to rely on. But it’s the third and fourth line that you’re going to have to get contributions from. Those are usually the lines that separate good teams from not-so-good teams. In a shortened season, you figure you have to rely on everybody to contribute on any given night. It’s going to be a grind, a sprint.”

When they’re playing with purpose and rhythm, the fourth line can create as many scoring chances as its other three counterparts. They force turnovers with their speed and blue-collar play. They throttle defensemen on the forecheck. They generate momentum for the other lines.

For all their assets, Julien believes they can be better.

“I thought that last year, they weren’t as good as the year before,” Julien said this week. “They need to find that chemistry and that energy that they gave us, that positive energy they gave our team. Maybe last year was tough because all three of those guys were looking for a new contract. Maybe they were pressing too much. But now is a situation where they can get back to doing what they did. They outworked every line they played against. They threw pucks to the net. They crashed the net. That’s how they got offensive results.”